How can 100% peanut butter have more protein than 100% peanuts

There's definitely some rounding going on because the peanut butter has 100.1g of nutrients per 100g of product. This isn't enough to explain the discrepancy. Adding up the nutrients on the roasted peanuts gives 95.4g. I think we can assume the other 4.6% is water. So perhaps more water has been driven off the peanut butter.

What I think is more likely (though could be additional) is that there's significantly less fat in the peanut butter (48.1% vs 51.7%). While this could be down to different varieties of peanut, I suspect some fat is removed in the processing, perhaps to avoid an oil slick on the surface.

Most likely of all is just different source data. Different peanuts may have been used in the calculations -- whether that is consistent with the actual ingredients used is another matter. In fact if you look at nutrition information for raw peanuts online, you'll get a range of values. There's nothing special about peanuts, the same is true for bananas. I'm sure if you look at the scientific literature on any foodstuff, you'll find a range of values published, reflecting natural variation as well as measurement variabilility -- this will then propagate to the values published to the consumer.

My guess is that the peanut butter is 100% peanuts but not 100% of the peanuts are being used in it.

That's like sea salt that is 100% from the Atlantic Ocean. It still contains a smaller amount of water (and consequently a larger amount of sodium) than the Atlantic Ocean does.

Or 100% pure orange juice which fortunately omits the orange peels.

Presuming that the nutrient labels are accurate (for some value of "accurate"), I can think of two reasons for the difference.

1. Nutrient labels are rounded very aggressively (as in, to the nearest multiple of 10). Thus, doing math on the numbers is likely to result in so much error propagation that any differences are meaningless.

2. Peanut butter generally does not include the paper skins, whereas roasted peanuts generally do include them. It doesn't seem like a large difference, until you try peanut butter that didn't remove the skins. (Hint: it was awful.)

The differences you see are probably mostly due to reason #1, with maybe a little bit of reason #2 showing through the inherent inaccuracies.

There are at least a dozen varieties of peanuts. Some are better for whole peanuts and others for peanut butter. Possibly there are some nutritional differences between varieties. Also the preparation could come into play, dry roasting vs oil roasting.

Different roasting techniques result in different protein amounts(as per this chart). https://www.healthaliciousness.com/nutritionfacts/nutrition-facts-compare.php

I would also guess that this is a result of the many different types of peanuts> Certain varieties are more likely to be peanut butter and others roasted and eaten by the handful,while other varieties are grown solely to be put into candy bars. However as the chart leads you to believe most of the data for different varieties may be averaged together. Thus, the difference is probably due to specific data for the specific varieties used plus the specific techniques in preparing them.

Also fun fact: oil roasted peanut butter tastes better as Alton Brown has explained in Good Eats and on his blog with youtube videos.

The reason is this; It was shown on an episode of Food Unwrapped. Peanuts are very high in fat but because of how we chew them and swallow we do not break down the structure enough to release all of the fat in them. So when testing fat content for peanut butter the fat content is higher because the nuts are broken down more thus releasing more fat from them. so in fact when people say nuts are fatty and bad for you they aren't actually that bad because you only get about a 3rd of the fat out of them

In addition to the other answers, different brands of 100% peanut butter contain rather different amounts of protein, fat etc per 100g.

Aldi's has 26g protein, 47g fat, of which 6g saturated, 9g carbohydrate, of which 4.8g sugars, 8g fibre, 6mg sodium and 650mg potassium.

Sanitarium's has Per 100g Energy (Cal) 612 Protein (g) 30.2, Fat (g) 49.4, of which saturated 4.8, trans, 0.0 polyunsaturated 3.9 monounsaturated 41 Cholesterol (mg) 0.0 Carbohydrate (g) 9.4, of which Sugars (g) 5.6 Dietary Fibre (g) 7.1 Sodium (mg) 5.0 Potassium (mg) 720. Link to Sanitarium 100% peanut butter ingredients

Sanitarium's no sugar, no salt peanut butter (but oil is added) somehow has more protein per 100g than their 100% peanut butter. enter link description here

Speculating about the causes, could be different sorts of peanuts, different ripeness, different roasting (makes more or less nutrients absorbable by the digestive tract) or just plain errors/lying about the ingredients.

I am not 100% sure. But as the link you provided for wholefoods states "No... Palm oil" this does not exclude additional peanut oil. Almost every recipe for Peanut Butter I can recall, calls for additional peanut oil.

It could be contamination. The lab tech who measured the peanuts surely would notice an insect or mouse tossed in with his peanuts. Unfortunately, the lab tech who received the peanut butter does not have that luxury. I know that is extremely common with grapes vs raisins. Nearly all commercial raisins have a non-trivial portion of insect matter. Ever thought about how raisins could be "sun-dried" inside?

Admittedly, however, I think it is more likely that some oil is either lost or skimmed off during the process to produce a thicker, less oily product. It also looks like they discard some fiber, probably when it jams the machine.